Hello I am trying to figure out which champion i would like to buy next and i would like some feedback on which one would be best to get because i have no clue at all i relize that they all are 3 very different champions but i have narrowed it down to these 3 and if anyone can give me some ideas on which one to pick then that would be greatly appretiated. Please own atleast 2 or more of them if you leave feedback, and if you could tell me what type of play styles and what not that i would be doing with them that would be great too. Thank you.

Xerath is basically an AP Nuker. He's all about those skilshots, but he has wonderful range. Very hard to use.
Twitch is a hypercarry/Stealth. He's the biggest glass cannon in the game. His entire means of survival depends on whether or not you catch them before they catch you. Buy tons of oracles and watch our for pink wards. Stay away from him because even most lvl 30s have trouble playing him well.
Malzahar would probably be your best choice. He does tons of damage and he's generally fun to play. Out of all of these 3, he's definitely the easiest to play.
You seem to have chosen 3 very difficult champions. I'd recommend going back and trying to find someone a bit more simpler.

i would chose xerath if u cant land skill shots and have good strategy ... if not then pick malz

Xerath.
He's the OP one.
Malz isn't that good and Twitch is only good late game.

well since i have morgana ive learned to be pretty good with skillshots so as long as im good with those i guess i should get xerath and i would choose other champs but atm i dont see any that i would like because i already have morg,nocturne, vlad, anivia